An analysis of the medial patellofemoral ligament length change pattern using open-MRI.

Recently, for a recurrent patellar dislocation, medial patellofemoral ligament (MPFL) reconstruction has come to be commonly performed, yet the precise in vivo MPFL biomechanics still remains to be clarified. The purpose of this study was to analyze the length change pattern of MPFL in vivo. The subjects were comprised of ten male and ten female healthy volunteers. The length of the MPFL was measured using an open-MRI both from a leg extended position and a highly knee-flexed position in order to analyze the length change pattern of the MPFL. The MPFL length for men and women resulted in an average of 52 ± 3 mm and 43 ± 2 mm at the knee extended position, respectively. The length change pattern of the MPFL presented a slight change at up to a flexion angle of 60° and a decrease at over 60°. In terms of morphology, the fiber bundle of the MPFL experienced linear tension at a knee flexion angle of 60°. We determined that the MPFL length in vivo exhibited a specific length change pattern. MPFL mainly contributes to the medial constraint of a patella with a knee flexion of 0° to 60°, wherein it is expected to have the strongest strain at 60°. However, more studies are needed to obtain a better understanding of cases with a history of patellar dislocation.